1. Field of the Invention
This invention relates to a syringe system for combining two dissimilar medicaments and, more particularly, to a structure for shielding a user of the syringe against aspirating or aerosoling solution upon withdrawal of the syringe cannula from a mixing vial.
2. Background Art
It is known to reconstitute drugs by combining and mixing isolated, dissimilar medicaments immediately prior to patient infusion. This procedure is common with drugs that are unstable or deteriorate in solution. By isolating the ingredients, whether two liquids or a liquid and solid, the storage life of the drug can be extended.
Normally a sterilized, evacuated dose vial contains a crystalline component and is hermetically sealed by a pierceable septum. The syringe cannula penetrates the septum to establish communication between the vial chamber and the inside of the syringe barrel. The barrel retains a complementary diluent which is injected into the vial. The vial containing the two components is agitated to completely dissolve the solid. The reconstituted solution is drawn back into the syringe barrel for administration to a patient.
The problem which the present invention obviates arises during the mixing of the isolated medicaments. Complete evacuation of the vial before injection of the diluent is seldom realized. There is thus a residual pressure in the vial after the solution dose is extracted. This residual pressure often causes discharge of some of the remaining solution in the vial through the rupture in the septum made by the cannula. Where the drug is toxic, as is common in oncological treatments, or is otherwise dangerous, this escaping solution may pose a health hazard to persons preparing, administering and receiving the injection.
Protective shields associated with the vial to limit exposure to the solution during admixture are known. In the structure depicted in U.S. Pat. No. 3,336,924 to Sarnoff et al, cooperating cover parts encase the vial and define a chamber to closely, guidingly accept the syringe barrel. A seal between the barrel and cover is effected with the syringe fully seated. Upon partial withdrawal of the cannula from the vial, the medicament freely aspirates into the cover chamber and is confined by the leading edge of the barrel. With the syringe separated from the cover, the medicament is unrestrained, escapes through the chamber opening, which is as large as the barrel diameter, and poses a potential hazard to the syringe operator and/or the person disposing of the used, covered vial.
Another structure that exemplifies the state of the art is described in U.S. Pat. No. 3,659,602, to Cloyd. Cloyd discloses a two component syringe with separate vials penetrable by a double-ended cannula. An adapter sleeve is associated with one of the vials and defines a socket which accepts the end of a stopper piston. To operate the syringe, the vial and sleeve are advanced axially towards each other until the vial bottoms in the socket, thus eliminating the socket. Upon unseating the Luer taper from the adapter sleeve, the sleeve passage is open to the atmosphere. One contends in Cloyd with essentially the same problems associated with the Sarnoff et al structure previously described.
Another problem that the prior art structures make no provision for arises after filling the syringe. During aspiration of the solution from the vial into the barrel, air bubbles may become entrained in the solution. Before infusion, it is common to discharge a small volume of the solution to expel the bubbles. With the prior structures, this generally takes place with the cannula exposed to the environment and subjects the user once again to possible solution exposure.
Expulsion of the drug with the entrained air into the syringe cover in Sarnoff et al, while temporarily shielding the user, accumulates additional solution in the syringe cover in addition to that aspirating from the vial. Escape of the solution from the syringe cover is unobstructed so that once again the user and/or the person subsequently disposing of the vial and cover are liable to come into contact with the solution.
The present invention is specifically directed to overcoming one or more of the above enumerated problems known in the prior structures.